This study proposes to deliver microbiological evidence that complete removal of carious dentin from human teeth is not necessary in order to prevent further progression of the disease, as long as the margins of a restoration are sealed against the ingress of bacterial nutrients. The concept of incomplete caries removal is not new, and has been convincingly supported by studies of Handelman, Mertz-Fairhurst and others. Nowadays, indirect pulp treatment is an accepted and advised option for treating deep carious lesions. In this procedure the carious dentin removal is left incomplete in order not to endanger pulpal health. One study also reports that carious dentin was left in 72% of cavities which were deemed to be caries free (Anderson '85). It is improbable to suggest that all these teeth then became non-vital! There is also indirect evidence from the literature to support this concept. However, it has not yet become the treatment of choice in general dental practice, although such treatment would certainly conserve more tooth tissue; be less traumatic for the patient; less time consuming for dentist and patient; perhaps less expensive; and be a treatment option in communities where access to care is problematic because of a lack of trained dental personnel. Biologically there are also several important questions to be answered. Current molecular techniques may provide definitive answers to the reduction in numbers and viability of the "entombed" microflora. This study aims to sample carious dentin (n=30) after incomplete caries removal at baseline and at 6 months after sealing, to investigate the residual bacteria, i.e. total bacterial load, distribution of various species and metabolic activity of the microbiota involved. Qualitative clinical and radiographic data will be complemented by current molecular techniques. Quantitative PCR and real-time RT-PCR will allow for quantitative analysis and reveal a more complete picture of the persistence of cariogenic bacteria. This investigation is a clinical and molecular re-entry study of sealing of caries, in support of a future full-scale clinical trial of incomplete caries removal.